Refining of bismuth alloys by halogenation



Oct. 11, 1960 H. MIRANDA FLORES ETAL 2,955,931

REFINING OF BISMUTI-l ALLOYS BY HALOGENATION Original Filed April 18, 1957 T S N SE $1 .5 0 G L A M p D EAW N VDT 1. A WW 1. Y R N E MM N 0 WE T Q2 r A WE U0 HRH United States Patent REFINING OF BISMUTH ALLOYS BY HALOGENATION Continuation of application Ser. No. 653,585, Apr. 18, 1957. This application Nov. 12, 1957, Ser. No.

4 Claims. (CI. 75-70) This invention relates to the refinin of metallic bismuth. More specifically, it relates to the production of relatively pure metallic bismuth by means of selective halogenation of metals present in bismuth alloys. The present invention further provides a method whereby the bismuth content of a molten alloy is maintained at a controlled level so that the selective halogenation r'eactionprogresses at a high rate.

I This application is a continuation of our application Serial No. 653,585, filed April 18, 1957, now abandoned. One common source of metallic bismuth in the dross from a lead refining operation. Snch dross normally contains relatively small amounts of bismuth of the order of 5% by weight along with varying amounts of lead, calcium and magnesium. The bismuth-containing dross is upgraded and smelted according to known procedures to yield a crude product assaying between 25 and 40% by weight of bismuth, the balance being primarily lead. The calcium and magnesium originally present are removed in the form of slags. After further treatment, such as by cupellation, more lead is removed so as to give a higher bismuth assay in the range of 50 to 65% by weight. Above this point, methods have been devised to purify the bismuth by the selective halogenation of the remaining lead, e.g., by contact with chlorine gas. Chlorination of the residual lead in the bismuth alloy forms molten lead chloride which separates out as a layer over the molten metal undergoing purification.

Bismuth alloys containing zinc, cadmium, tin, alumiuum and other metals are by-products of various metallurgical processes and such alloys may also be processed by selective halogenation to produce metallic bismuth of high purity. g

It has now been found that the selective halogenation rate of a bismuth alloy increases markedly and unexpectedly when the molten alloy contains more than 85 and preferably between about 90 and 98% by weight of bismuth. Utilizing this discovery, which appears to be contrary to the law of mass action, it has become possible to devise processes for the accelerated recovery of bismuth from alloys containing less than 85% by weight of bismuth. Furthermore, the discovery makes it feasible to produce purified bismuth from its alloys on a semicontinuous or continuous basis, whereas batchwise operation has been common practice.

Accordingly, a principal object of the invention is 'to provide a process for the production of purified metallic bismuth from a bismuth alloy by selective halogenation at an accelerated rate.

Another important object is to carry out the selective halogenation of bismuth alloys on at least a semi-continuous basis which has obvious economic benefits.

' These and other objects and advantages of the inventi'on will become apparent from the following description, taken in connection with the drawing which is a schematic ice 2 flow-sheet illustrating the invention in the form of a semi-continuous process.

In accordance with the invention, bismuth alloy's'coritaining less than 85%, usually in the range of 50 to 65%, by weight of bismuth are periodically or continuously added to a molten mass of bismuth alloy under going selective halogenation and containing over 85%, preferably at least 90%, byweight of bismuth. For conveneince, hereinafter the starting material, i.e., a bismuth alloy containing less than 85% by weight of bismuth will be referred to as the feed alloy and the molten mass undergoing selective halogenation and containing over 85% by Weight of bismuth will be referred to as the pool alloy.

. By adding the feed alloy in an amount and at at rate to the molten pool alloy so that the bismuth content of the pool alloy is maintained over 85%, preferably at least 90%, by weight, the refining of the feed alloy to produce high-purity (over 99% by weight) bismuth is markedly accelerated.

While the selective halogenation of the metals other than bismuth present in the pool alloy may be carried out with any of the halogens, chlorine is commonlyselected because of its relatively low cost. The halogenation, as is known, is conducted generally at a temperature of at least 500 C., and preferably in the range of 550 to 700 C.

As already mentioned, bismuth is frequently derived from feed alloys in which lead is the principal metal alloyed with bismuth. Such feed alloys may be selectively chlorinated pursuant to this invention to convert the lead content to lead chloride at a more rapid-rate than has been possible heretofore. The lead chloride forms a molten phase which in the course of the halogenation reaction rises to the top of the molten mass of pool alloy. The supernatant lead chloride is readily separated from the molten pool alloy.

It would be expected from the law' of mass action that the chlorination rate would be the greatest when the proportion of unconverted lead in the reaction zone was the largest, and that this chlorination rate would diminish as the lead content decreased. Contrary to this expectation, however, the chlorination rate, i.e., the weight of lead converted to lead chloride per hour, has been found to increase sharply at low lead contents (below 15% by weight) or high bismuth contents over by Weight.

Referring to the drawing, the feed alloy is maintained in the molten state in vessel 10 which may be externally heated. Pump 12 supplies the feed alloy-to reaction vessel 14 through pipe 16, the timing of feed being controlled in a manner hereinafter indicated.

Reaction vessel 14, which may be externally heated is provided with at least one pipe 18 through which gaseous chlorine is passed downwardly into the-molten pool alloy in the vessel. Reactor 14 has one portion ofthe peripheral edge thereof depressed and formed into over= flow lip 26 so that the lead chloride whichforms in the reaction and rises to the surface of the molten pool alloy may overflow into a suitable storage vessel. :Reactor 14 is also provided, in the lower portion thereof, with valved outlet 22 for the Withdrawal of pool alloy which may flow through pipe 24 to another reactor like 're= actor 14 so as to continue the selective halogenation until the lower molten mass is substantially pure bismuth; As chlorination proceeds, the lead chloride which is pro duced forms a molten layer 26 over the molten'mass 28 of pool alloy with a bismuth content over 85% by weight. Although the feed alloy contains less than 85 and usually less than 65%, by weight of bismuth, the

desired high reaction rate is achieved addition of the feed alloy to the pool alloy so that the bismuth content of the pool alloy is always above 85%, preferably at least 90%, by weight.

In a specific example of the invention, reactor 14 is filled to a level B slightly. below the overflow level A of lip 20 with poolalloy containing about 91% by weight 'while the level B of the pool alloy drops to level C because of the elimination of lead therefrom. At level 0, the pool alloy, has a bismuth concentration of about 96% by weight, whereupon level controller 30 electrically operates pump 12 to supply molten feed alloy analyzing about 60% by weight of bismuth and 40% by. weight of lead from vessel '10 through pipe 16 to reactor 14. When the pool alloy'rises to level B, level controller 36 automaticallystops pump 12. While the level of the pool alloy i being raised by the addition of feed alloy, molten lead chloride is being discharged through lip 20. By adding 1 part by weight of feed alloy to each 5 parts of pool alloy when down to level C, i.e., when the bismuth con centration is 96% by Weight, the pool alloy will still contain at least 90% by weight of bismuth when level B is restored. 5

Of course, the chlorination continues to remove lead from the pool alloy with the result that level B again moves downwardly while the layer of lead chloride in creases. 'As before, level controller 30 activates pump 12 when the surface of the pool alloy drops to level C. Each succeeding time that this happens, the bismuth concentration ofthe pool alloy is higher than it was the previous time. Thus, while the bismuth concentration was 96% by 'weight the first time that the pool alloy contracted to level C, this concentration increases each succeeding time until a bismuth concentration of well over 99% by weight is reached. At this point, a sample of the pool alloy, now substantially pure bismuth, is taken and cast into a small bar. typical fracture of pure bismuth, level controller 30 is turned off before it again starts up pump 12 so as to prevent the flow of feed allov into reactor 14. Molten bismuth is now discharged as refined product by controlling the .of say 95% by weightbisrhuth content, the continuing flow of this alloy is diverted to another finishingreactor. After the first finishing reactor has discharged its batch of refined bismuth, the flow of pool alloy is again directed thereto. "In the meantime, the pool alloy collected in another of the finishing reactors is selectively chlorinated to yield bismuth of the desired purity. In this way, the

- operation of reactor 14 can be made continuous with reunreacted chlorine escaped from the molten mass. Dur- If the bar breaks with the through valved outlet 22 and pipe 24 into suitable containers. However, not all of the molten bismuth is removed from reactor 14 since part is required to form the original pool alloy with a bismuth content of about 91% by weight for the next refining cycle. For this purpose, there is retained in reactor 14 a quantity of molten bismuth such that when l partby weight of the feed alloy (60% by Weight of bismuth) is added for each 3 /2 p rts of retained pure bismuth, the surface of the resulting pool alloy will again return to level B. The foregoing refining cycle at this point begins to repeat itself.

ing the first 55 hours of chlorination, lead was eliminated from the alloy at an approximately uniform rate of 10 kilogramsper hour. At this point, the molten alloy undergoing chlorination had a composition of 86.7% by Weight of bismuth and 13.3% by weight of lead. During the next 4 hours of chlorination, the average rate of lead elimination was 13 kilograms per hour; at the end of 59 hours, the molten alloy contained 90.1% 'by weight of bismuth and 9.9% by weight of lead. In 3 hours of further chlorination, the molten material gave an analysis of 99.4% by weight of bismuth, the average rate of lead elimination in this final period'being 39 kilograms per hour.

From the foregoing data, it is clear that the process of this invention makes it possible to carry out the selective halogenation of bismuth alloys containing less than 85% by weight of bismuth under conditions giving significantly higher rates of reaction which are unexpectedly characteristic of alloys having a bismuth content of over 85%, preferably at least about 90%, by weight. g In view of the various modifications of the invention which will occur to thoseskilled in the art upon consideration of the foregoing disclosure without departing from the spirit or scope thereof, only such limitations should be imposed as are indicated by the appended claims.

What is claimed is: i

l. The process of chlorinating a. feed bismuth alloy having a bismuth content of less than 85% by weight and containing lead as the predominant alloying ingredient,

i which comprises the steps of adding said feed bismuth The preceding illustrative operation of the invention 2 i is semi-continuous in that the feed alloy is added. and the refined bismuth is wit drawn, from re ctor 14 intermittently. 'Either the addition or the withdrawal may be continuous. In fact, both the addition and the withdrawal may be made continuous. Where continuous withdrawal of the pool alloy from reactor 14 i desired, it is clearly not practical to obtain directly a bismuth product of over 99% by weight purity. In such instance, the rate of addition of feed alloy and the rate of withdrawal of pool alloy may be correlated with the rate of chlorination so that the pool alloy is maint ined at a substantially. constant bismuth concentration over 85 preferably in the rangeof 90 to 98%, by weight, say at a alloy to a molten metal pool maintained during such addition of feed bismuth alloy at a bismuth content above by weight and passing chlorine gas into the combined mass of molten metal while maintining said metal at a temperature of from 500 to 700 C. to selectively chlorinate the lead contained therein at an accelerated rate.

2. The process of claim -1 wherein the feed bismuth alloy initially-has a bismuth content ranging from 50 to 65%. a a

3. The process of claim 1 wherein the molten pool subjected to chlorination contains bismuth in the amount ofat least a 4. The process of chlorinating having a bismuth content between 50 and 85% by weight and containing lead as the predominant alloying ingredient, which comprises the steps of adding said feed bismuth alloy to a molten metal pool maintained during such addia feed bismuth alloy tion of feed bismuth alloy at a bismuth content above References Cited in the file of this patent 85% by welght, passing ehlonne gets 1nto the combined UNITED STATES PATENTS mass of molten metal While maintaining said metal at a temperature of from 500 to 700 0. to selectively chlo- 1,778,292 Dopahue Oct 14, 0 rinate the lead contained therein at an accelerated rate, 5 1,816,620 Smfth et a1 July 1931 withdrawing lead chloride which separates from the re- 118701388 Smlth g- 9 action mixture as it is formed and intermittently with- 2,205,387 Betterton et 111116 40 drawing a portion of the remaining molten bismuth ma- 2,342,733 Guyard Feb. 29, 1944 terial when the bismuth content thereof reaches a value 2,793,572 Hudson et M y 1 of at least 98% by weight. 10 2,783,991 Morize Mar. 5, 1957 

1. THE PROCESS OF CHLORINATING A FEED BISMUTH ALLOY HAVING A BISMUTH CONTENT OF LESS THAN 85% BY WEIGHT AND CONTAINING LEAD AS THE PREDOMINANT ALLOYING INGREDIENT, WHICH COMPRISES THE STEPS OF ADDING SAID FEED BISMUTH ALLOY TO A MOLTEN POOL MAINTAINED DURING SUCH ADDITION OF FEED BISMUTH ALLOY AT A BISMUTH CONTENT ABOVE 85% BY WEIGHT AND PASSING CHLORINE GAS INTO THE COMBINED MASS OF MOLTEN METAL WHILE MAINTAINING SAID METAL AT A TEMPERATURE OF FROM 500 TO 700*C. TO SELECTIVELY CHLORINATE THE LEAD CONTAINED THEREIN AT AN ACCELERATED RATE. 